Trade-offs and upper limits to signal performance during close-range vocal competition in gray tree frogs hyla...

Performance limitations on signal production constrain signal evolution. Variation in signaling performance may be related to signaler quality and therefore is likely to be a salient aspect of communication systems. When multiple signal components are involved in communication, there may be trade-offs between components, and performance can be measured as the degree to which signalers approach the upper limits of the trade-off function. We examined vocal performance in the gray tree frog Hyla versicolor, in which females prefer values of call duration and rate exceeding the usual range of variation within and among males. We recorded interactions between pairs of males calling on mobile platforms that allowed us to manipulate intermale distance and place males in highly competitive environments. We found that, although there was a clear upper boundary on the ability of males to maximize call duration and call rate simultaneously, call effort did not remain constant in this highly competitive situation. Our estimates of an upper limit to vocal performance were corroborated by analyses of calling behavior in the context of close-range mate attraction. We discuss potential constraints on signaling performance and the relevance of this measure of performance for both intrasexual and intersexual communication.